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INTRODUCTION 

This is the Environmental Protection Agency’s (EPA or the Agency) Final Work Plan (FWP) for 

the registration review of imazethapyr. This work plan addresses public comments received 

concerning the Preliminary Work Plan (PWP), which was posted in the imazethapyr registration 

review docket (EPA-HQ-OPP-2013-0774). This case includes the active ingredients imazethapyr 

and imazethapyr ammonium salt. Imazethapyr and imazethapyr ammonium salt are systemic 

herbicides of the imidazolinone herbicide family. They are registered for use as selective 

herbicides to control grasses and broadleaf weeds in certain agricultural use sites and are also 

registered for use in certain non-agricultural use sites. Throughout this FWP, EPA will refer to 

the two active ingredients in the case collectively as imazethapyr. 

The Agency is implementing the registration review program pursuant to Section 3(g) of the 

Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), and will review each registered 

pesticide every 15 years to determine whether it continues to meet the FIFRA standard for 

registration. Changes in science, public policy, and pesticide use practices occur over time. The 

registration review program is intended to make sure that, as the ability to assess risk evolves and 

as policies and practices change, all registered pesticides continue to meet the statutory standard. 

The public phase of registration review begins when the initial docket is opened for each case. 

Information on this program is provided on the Agency’s website.1

The FWP begins with any updates since the PWP was issued. Next is a summary of substantive 

comments received during the public comment period for the PWP concerning anticipated data 

needs, expected risk assessments, or the estimated timeline identified in the PWP, and a 

summary of the Agency’s responses to those comments. This section is followed by registration 

review planned data needs, risk assessments expected to be conducted, and the projected 

registration review timeline for imazethapyr. Lastly, there is a discussion of next steps. 

UPDATES SINCE THE PWP WAS ISSUED 

There are no additional updates on imazethapyr since the PWP. 

SUMMARY OF COMMENTS AND AGENCY RESPONSES 

During the 60-day public comment period on the imazethapyr Preliminary Work Plan, which 

opened on March 28, 2014 and closed on May 27, 2014, the Agency received public comments 

pertaining to the imazethapyr case from four stakeholders. Comments were submitted by BASF 

Corporation (BASF), the California Department of Pesticide Regulation (CDPR), the FIFRA 

Endangered Species Task Force (FESTF), and the National Alfalfa & Forage Alliance (NAFA). 

The comments do not address the timeline or the planned risk assessments described in the PWP, 

but they do address the planned ecological data requirements. In the PWP, EPA also solicited 

comments on the specific topics of environmental justice, water quality concerns, and trade 

irritants; EPA received groundwater monitoring data from CDPR, but no other comments or 

information were received on those issues. 

 

1

 http://www.epa.gov/oppsrrd1/registration_review/ 
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This section does not capture every comment made about the PWP nor all of the Agency’s 

responses. Summarized below are public comments that resulted in changes to the anticipated 

registration review data needs or are of a broader regulatory nature. Public comments and EPA 

responses in their entirety are located in the docket EPA-HQ-OPP-2013-0774. Summarized 

public comments and Agency responses related to the anticipated ecological risk assessment or 

data needs are in the Response to Public Comments on the Imazethapyr and Imazethapyr 

Ammonium Salt Registration Review Problem Formulation. In response to comments regarding 

use and usage information, EPA has updated the BEAD Chemical Profile (BCP) for Registration 

Review Imazethapyr Chemical Case [Includes Imazethapyr (128922) and Imazethapyr, 

Ammonium Salt (128923)]. 

Comments submitted by NAFA in EPA-HQ-OPP-2013-0774-0012. 

1. Comment: NAFA submitted comments expressing support for the continued registration of 

imazethapyr for use in alfalfa seed and hay production and provided information about the uses 

and benefits of imazethapyr. They discussed the importance of alfalfa seed and hay as rotational 

crops, discussed the high degree of weed control that alfalfa hay/seed crops require, and the 

importance of weed-free alfalfa hay/seed for export. They also discussed the way alfalfa for hay 

is planted which makes cultivation unsuitable for control of weeds, listed some problems with 

herbicides that are alternatives to imazethapyr, discussed some reasons glyphosate resistant 

alfalfa and glyphosate use are not replacements for imazethapyr, and discussed the importance 

of the residual weed control offered by imazethapyr. They also commented on the importance of 

rotating and tank mixing herbicides with different modes of action as an important tool for 

managing herbicide resistant weeds in all crops, and the importance to alfalfa growers of 

imazethapyr’s mode of action (ALS inhibitor).

Response: EPA thanks NAFA for their comments, and will consider the information during 

registration review. 

Comments submitted by BASF in EPA-HQ-OPP-2013-0774-0015. 

2. Comment: BASF submitted comments pertaining to the anticipated data needs listed in the 

imazethapyr PWP and the EFED Problem Formulation.

Response: Agency responses related to each comment from BASF regarding anticipated data 

needs are located in the Response to Public Comments on the Imazethapyr and Imazethapyr 

Ammonium Salt Registration Review Problem Formulation. The comments from BASF 

resulted in two changes pertaining to the anticipated data needs listed in the PWP: 1) the 

previously anticipated requirement for a study of honey bee toxicity from residues on foliage 

(guideline number 850.3030) has been removed from the list of planned data needs in the 

FWP and 2) EPA is correcting the test material for the non-guideline honeybee larval toxicity 

study; this study should be conducted with the technical grade active ingredient (TGAI), 

rather than a typical end-use product (TEP) as previously listed in the PWP. 

3. Comment: BASF submitted a comment on use and usage information, stating that they 

“would like to correct the reference to corn and rice as genetically modified. Both corn and 
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rice, as listed on imazethapyr-based products, are herbicide tolerant but non-genetically 

modified crops (non-GM).”

Response: EPA has updated the BEAD Chemical Profile (BCP) for the imazethapyr case to 

remove references to corn and rice as genetically modified. The updated BCP will be posted 

in the imazethapyr registration review docket. 

PLANNED DATA NEEDS 

Table 1 below summarizes the planned data needs for imazethapyr based on the Registration 

Review Problem Formulation for Imazethapyr and Imazethapyr Ammonium Salt and 

Imazethapyr Human Health Assessment Scoping Document in Support of Registration Review, as 

well as the Response to Public Comments on the Imazethapyr and Imazethapyr Ammonium Salt 

Registration Review Problem Formulation. The table has been updated since the PWP to reflect 

public comments which resulted in changes to the data needs. The previously anticipated 

requirement for a study of honey bee toxicity of residues on foliage (guideline number 850.3030) 

has been removed from the list of planned data needs in Table 1 below. Table 1 below also 

clarifies that both an acute and a chronic larval toxicity studies are needed and corrects the test 

material for both; these studies should be conducted with TGAI, rather than TEP as previously 

listed in the PWP. In addition, the standard timeframe for the honey bee larval chronic oral 

toxicity has been listed as twenty-four months. 

Table 1: Planned Data Needs for the Imazethapyr Registration Review Case 

Guideline 

Number2 Study Title Test Material 

Estimated 

Timeframe 

(Months from 

receipt of DCI) 

Anticipated Data Needs for the Parent

850.3020 Honey bee acute contact toxicity 

Imazethapyr 

TEP or 

imazethapyr 

ammonium salt 

TEP 

12 

Nonguideline3 Honey bee acute oral toxicity 

Imazethapyr 

TEP or 

imazethapyr 

ammonium salt 

TEP 

12 

 

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 On June 27, 2012, EPA announced certain revisions in harmonized guideline series 850 – Ecological Effects Tests 

– including renumbering and other designations or changes for some guideline studies. See “Final Test 

Guidelines; OCSPP 850 Series; Notice of Availability” 77 FR 38282, June 27, 2012. 

http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPPT-2009-0154-0028 3

 Although an OCSPP test guideline is not available, OECD 213 may be used. 
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Table 1: Planned Data Needs for the Imazethapyr Registration Review Case 

Guideline 

Number2 Study Title Test Material 

Estimated 

Timeframe 

(Months from 

receipt of DCI) 

Nonguideline4 Honey bee larval acute oral toxicity 

Imazethapyr 

TGAI or 

imazethapyr 

ammonium salt 

TGAI 

12 

Nonguideline5,6 Honey bee larval chronic oral toxicity 

Imazethapyr 

TGAI or 

imazethapyr 

ammonium salt 

TGAI 

24 

850.4100 Terrestrial plant toxicity, seedling emergence 

Imazethapyr 

TEP and 

imazethapyr 

ammonium salt 

TEP 

12 

850.4150 Terrestrial plant toxicity, vegetative vigor

Imazethapyr 

TEP and 

imazethapyr 

ammonium salt 

TEP 

12 

Anticipated Data Needs for the CL266858 Degradate

850.4400 Aquatic plant growth (aquatic vascular plant 

toxicity) 

Degradate 

CL266858 12 

RISK ASSESSMENTS FOR REGISTRATION REVIEW

During registration review, the Agency will conduct a comprehensive ecological risk assessment, 

including an endangered species assessment, for all uses of imazethapyr. For human health, EPA 

has determined that a qualitative assessment is sufficient based on the low toxicity of 

imazethapyr; therefore, EPA will not conduct revised quantitative dietary, residential, and 

occupational risk assessments during registration review. 

Table 2 below summarizes the planned registration review risk assessments based on the EFED 

Problem Formulation and HED Scoping Document; the planned assessments have not changed 

from what was included in the PWP. 

 

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 Although an OCSPP test guideline is not available, OECD 237 may be used. 

5 The November 2013 draft OECD protocol for a honey bee brood test using repeated doses may be used for this 

study. Please see 

http://www.oecd.org/env/ehs/testing/Draft_GD_honeybees_rep_exp_for_2nd_CR_25_November_2013.pdf for 

details.

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 A protocol should be submitted to the Agency for review and approval prior to study initiation. 
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Table 2: Planned Risk Assessments for the Imazethapyr Registration Review 

Type of Risk Assessment Conduct? Notes 

Ecological and Environmental Fate 

Comprehensive ecological 

(species to be assessed 

include terrestrial and aquatic 

organisms), including 

endangered species 

Yes EPA anticipates conducting an updated 

comprehensive ecological risk assessment during 

registration review. The new assessment will 

incorporate the most up-to-date modeling 

methodologies, updated toxicological endpoints, and 

data submitted under the anticipated registration 

review data call-in. 

Incidents Will check for 

updates 

For a discussion of reported ecological incidents, see 

page 19 of the Problem Formulation. 

Human Health 

Dietary 

Food No The most recent dietary exposure assessment was 

conducted for the 2005 human health risk assessment. 

No dietary risks of concern were identified. Since it 

has been determined that a qualitative assessment is 

sufficient based on the low toxicity of imazethapyr, a 

quantitative dietary exposure assessment is not 

needed for registration review. 

Drinking water No 

Occupational 

Handlers (mixers, loaders, 

applicators) 

No The most recent occupational and residential exposure 

assessment was conducted for the November 2005 

human health risk assessment. No occupational risks 

of concern were identified. Since it has been 

determined that a qualitative assessment is sufficient 

based on the low toxicity of imazethapyr, quantitative 

occupational exposure assessments are not needed for 

registration review. 

Post-application No 

Residential 

Handlers No The most recent occupational and residential exposure 

assessment was conducted for the November 2005 

human health risk assessment. No risks of concern 

were identified. Residential exposure scenarios have 

not been assessed; however, since it has been 

determined that a qualitative assessment is sufficient 

based on the low toxicity of imazethapyr, quantitative 

occupational and residential exposure assessments are 

not needed for registration review. 

Post-application No 

Other 
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Aggregate No Evaluates the combined risk from dietary and 

residential exposures. The most recent aggregate 

exposure assessment was conducted for the 

November 2005 human health risk assessment. No 

risks of concern were identified. Since it has been 

determined that a qualitative assessment is sufficient 

based on the low toxicity of imazethapyr, quantitative 

aggregate assessments are not needed for registration 

review. 

Cumulative No Not applicable. Imazethapyr and imazethapyr 

ammonium salt have not been identified as members 

of a cumulative group that shares a common 

mechanism of toxicity. 

Tolerances Yes Tolerances for imazethapyr are established in 40 CFR 

§180.447. These include a tolerance for imazethapyr 

on imported canola. During registration review, EPA 

plans to update the tolerance expression for 

harmonization purposes and to conform to current 

EPA policy. 

Incidents Will check for 

updates 

For a discussion of reported human incidents, see 

pages 7-8 of the Scoping Document and the 

Imazethapyr: Tier 1 Review of Human Incidents. 

TIMELINE

EPA has created the following estimated timeline for the completion of the imazethapyr 

registration review in Table 3 below. The projected timeline has been updated since the PWP to 

reflect the standard time that may be necessary to conduct the honey bee larval chronic oral 

toxicity study, which is twenty-four months. 

Table 3: Registration Review for Imazethapyr – Projected Registration Review Timeline

Activities Estimated Date 

Opening the Docket 

Open Docket and 60-day Public Comment Period Mar. 2014 – Completed 

Close Public Comment May 2014 – Completed 

Case Development 

Final Work Plan Sept. 2014 – Completed 

Issue DCI 2014 Oct. – Dec. 

Data Submission 2016 Oct. – Dec. 

60-day Public Comment Period for Draft Risk Assessments 2018 April - June 

Registration Review Decision 

60-day Public Comment Period for Proposed Registration Review 

Decision 

2019 Jan. - March 

Registration Review Decision and Begin Post-Decision Follow-up 2020 

Total (years) 6 
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NEXT STEPS 

As noted previously, the Agency plans to require several ecological effects studies for 

imazethapyr through a Data Call-In Notice, expected to be issued in late 2014.